The present invention relates in general to automotive air conditioning systems, and, more specifically, to an expansion valve with reduced hissing noise.
A thermal, or thermostatic, expansion valve (TXV) is widely used in air conditioning systems to control the superheat at the evaporator outlet. A TXV throttles refrigerant and generates a hissing noise. The hiss noise is especially prominent when the TXV first opens, e.g., upon opening during normal cycling of the valve or when the compressor is first started. The repetitive nature of the cycling of the TXV during system operation makes the hiss noise especially undesirable.
To resolve this problem, the size of the valve opening may be reduced by design, but this may unduly limit the cool-down performance of the system. Furthermore, it does not resolve the issue of rapid valve opening at the compressor startup and thus has limited beneficial effect. Another solution to this problem has been to add screens at the TXV inlets and outlets, but empirical evidence shows that such screens have only a limited effect in reducing the hiss noise.
Another approach has been to slow down or delay the opening of the TXV, thereby allowing more time for the high pressure side of the refrigerant loop to rise up. The system reaches a more sub-cooled state before allowing a high rate of flow through the TXV, thereby absorbing residual vapor, reducing the initial refrigerant flow rate, and reducing hiss. As disclosed in Lou et al, U.S. application Ser. No. 11/893,691, filed Aug. 17, 2007, entitled “Thermostatic Expansion Valve,” the use of a restricted flow between the evaporator outlet and the pressure chamber in the charge assembly controlling the opening of the TXV is one way to achieve the desired delay. Another solution is given by Lou et al, U.S. application Ser. No. 12/123,865, filed May 20, 2008, entitled “Air Conditioning Circuit Control Using a Thermostatic Expansion Valve and Sequence Valve,” wherein a sequence valve is added in series with the TXV to prevent flow through the TXV until the desired sub-cooled state is reached.
Although the foregoing measures achieve desirable reductions in hiss noise, they add complexity and cost over expansion valves without these features. It would be desirable to reduce the added cost and complexity while maintaining the desirable reduction in hiss from the TXV.